Why would you think dead grass is harmful? It's not dead grass that is harmful. The poison that kills the grass is harmful.

Chocolate is toxic to dogs, but that doesn't mean it's dangerous to us. Again, you can't just rely on your gut feeling for this kind of stuff.

Roundup is toxic to humans as are most if not all herbicides. I think it would be better to assume anything that can kill grass is toxic to humans unless there is significant research proving this to not be true. I would rather see people err on the side of caution in this area.

I would not put antibiotics, GMO or gluten in the same basket, however even if (imo) pretty valid concerns arise from the population, these are still used widely.

I don't understand this sentiment, why is organic so quickly associated why unscientific bullshit like anti-vaccine? Maybe it's specific to the US, but here in France even if historically there is a lot of snake-oil products associated with "natural" things, organic is a strict regulated label, and apart for some products (like wine), does not cause much debate in the "scientific-minded" crowd (except for GMO) for environmental and health benefits.